Nicotine Addiction Is a Serious Health Problem in the United States. Animal Models of Nicotine Addiction. This proposal will make use of transgenic mice lacking the Beta 2 subunit of the neuronal nicotinic acetylcholine receptor (nAChR) that no longer have any high affinity nicotine binding sites in the brain, to determine the role of the high affinity nicotine receptor in nicotine addiction. These studies will help define the precise molecular basis for nicotine addiction, and may provide tools that will allow a pharmacological treatment of this addiction. Three behavioral models of addiction (place preference, selective drinking and locomotor sensitization) will be used to determine whether mice lacking the high affinity nicotine receptors are still sensitive to the addictive effects of nicotine. In addition, the effects of nicotine on anxiety and antinociception will be analyzed in these transgenic animals. We will also attempt to compensate for deficits in animals lacking the Beta 2 subunit of the nAChR by overexpressing the Beta 4 subunit in the brains of these mice, allowing a molecular dissection of the roles of the different subunits of the nAChR in addictive behavior. As nicotine is able to regulate dopamine release in the nucleus accumbens and the ventral tegmental areas, brain area implicated in the addictive properties of several drugs of abuses, the effect of amphetamine, cocaine and ethanol of the behavior of Beta 2 subunit mutant mice will be examined. The specificity of existing nicotinic agonists for the different subtypes of the nAChR will be examined by comparing the binding of these agonists in the brains of wild type and Beta 2 subunit mutant mice. Finally, changes in neurotransmitter systems that can normally be modulated by nicotine treatment will be examined using equilibrium binding studies and essays of choline acetyltransferase assays. These experiments are designed to determine the precise role of a defined subunit of the nAChR in several behaviors that contribute to nicotine addiction in humans, with the goal of defining the molecular substrate of nicotine addiction.